I've never been asked to screen print on a sweater, but I don't see why you couldn't. I'd be concerned about any amount of fine detail because of the weave of a typical sweater. Big spot colors should work.
You mentioned hoodie in the title. If you meant sweat shirt instead of sweater, then you probably could use about any method, depending on color. I primarily screen print, but on hoodies and other sweatshirts, especially dark ones, I sometimes go with plastisol transfers or even CadCut Vinyl if its a really simple design. Depending on the design, I think a heat transfer that might be too thick for a t-shirt, actually looks and feels better and more at home on a nice thick fleece.
We screen print onto hoodies all the time, but keep in mind sweaters with zippers/ pockets may need special consideration with the design if you are thinking of printing around or over the seams and the zips. Covered zippers are printed over more easily than non-covered, but the design can/ will print with some imperfections as the zippers/ pockets keep the screen from sitting right flush on the fabric around them.
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